Koa – Next-generation web framework for Node.js

by m0hit • 13 years ago

281 121 13 years ago

quarterto3• 13 years ago

0s: "next generation web framework for node.js" (oh god, not another)

5s: "designed by the team behind Express" (wait what?)

6s: "Through leveraging generators Koa allows you to ditch callbacks" (wow, ok. oh hey, that makes "next generation" not just marketing fluff)

18s:

  app.use(function *(next){
    var start = new Date;
    yield next;
    var ms = new Date - start;
    this.set('X-Response-Time', ms + 'ms');
  });

(oh sweeet)

mateuszf• 13 years ago

So, does node support generators out of the box?

quarterto3• 13 years ago

It's behind a flag (--harmony-generators) in 0.11 (current stable is 0.10, hence my "next generation" comment).

FooBarWidget• 13 years ago

Reading this comment makes me sad. Does this mean you would have immediately closed the tab, irregardless of technology, if they didn't namedrop?

quarterto3• 13 years ago

I was already giving it the benefit of the doubt by reading any further than "next generation web framework for node.js".

usethis• 13 years ago

it's because of the hyperbole:

next generation web framework for node.js

I don't think they need that, just list the stand-out features first. And yes, referring to past accomplishments does give it more credibility.

mathrawka• 13 years ago

Too many things claim to be a "next generation framework", that it usually is a let down because it is just a rehash of something.

But this is something new that looks like it can be good. I've been wondering when it would be announced, as TJ has been working on it for a while: https://github.com/visionmedia?tab=activity

RivieraKid• 13 years ago

I would.

sergiotapia• 13 years ago

Offtopic: *irregardless is not a word, Just use regardless.

tolas• 13 years ago

You don't believe in social proof and a history of success?

dlau1• 13 years ago

It looks almost like if they rewrote express for generator functions

I can't wait to drop this in to one of my projects!

ds_10• 13 years ago

That's pretty much what they did (and connect, which was the foundation of express and since bought by senchalabs).

Gigablah• 13 years ago

Saw something similar in Martini (golang):

https://github.com/codegangsta/martini#next

    // log before and after a request
    m.Use(func(c martini.Context, log *log.Logger){
      log.Println("before a request")

      c.Next()

      log.Println("after a request")
    })

bjconlan• 13 years ago

I don't think this yields the current thread/routine though does it? I think what you are seeing here is closer to express':

  function(req, res, next) {
    console.log('before');
    next(); // go to the next middleware handler
    console.log('after the middleware stack has been traversed');  
  }

flym4n• 13 years ago

That's using a callback, like express or connect does. What's new in koa is the use of js generators

joenied• 13 years ago

I found the GIF on this page explains it pretty good: https://github.com/koajs/koa/blob/master/docs/guide.md

bsiddiqui• 13 years ago

pretty well

deif2• 13 years ago

I have some questions about this:

1. The FAQ gives a political answer about the status of Express but I imagine that Express will not be actively maintained any more. Correct?

2. If focus is now on Koa, why the name change from Express when it is already a huge name for node frameworks?

3. If a new developer sees Express and Koa, would they immediately know which one is being focused on?

Basically I'm wondering why it couldn't be called Express 3.0 (or 4.0).

ds_10• 13 years ago

I understand it's due to connect being bought by sencha. The FAQ states it's more like connect, with some express goodies moved to the middleware level.

deif2• 13 years ago

But express was connect with some extra goodies on top. Surely this is an iteration upon express?

I guess I'm more concerned about the marketing of this framework as there's now two names for the same thing except one is newer than the other. As a dirty analogy - if jQuery started to support yields instead of function callbacks, do they change the name of the library?

Looking at the syntax of Koa, it's still express except it looks nicer because there's no callbacks. What was the reasoning for ditching the big name? It can't be just for that.

enome• 13 years ago

My guess is that because Express and Connect aren't really big frameworks changing something fundamental as the middleware API would break all backwards compatibility. So you'll end up with a different framework anyway. This way people that like generator middleware can pick koa and if you prefer the old style middleware you can still use Express.js.

I also see pull requests getting merged into Express.js on almost a daily base. So I am not really worried about it dying anything soon. Most of the road map items for express are about extracting it's features into separate modules as well. Which means they are aiming at making the Express core even smaller and less opinionated.

bwilliams3• 13 years ago

Koa is only usable with >= 11.9 behind the --harmony flag, I doubt they'd want to release a new version of Express that most people can't/won't even use.

jongleberry5• 13 years ago

you can also use it with > 0.8 with https://github.com/TooTallNate/gnode

tjholowaychuk3• 13 years ago

Express is still maintained, by a bunch of us, but personally I'll be focusing mostly on Koa. They're separate because conceptually Koa is quite different, the migration from the would-be Express 3.0 -> 4.0 would mean rewriting the app

camus2• 13 years ago

If TJ is on board that's the only information you need to know, you cant go wrong with any code that guy writes.

mradmin4• 13 years ago

I have utmost respect for TJ and his work but I am not a fan of his yoda style programming :(

ds_10• 13 years ago

What do you mean by that? if (constant == variable) type conditions?

tjholowaychuk3• 13 years ago

haha I've grown to prefer it, sort of like regular conditionals vs postfix conditionals, you set up the expectation first:

if (user.isAuthenticated) doSomething()

doSomething() if (user.isAuthenticated)

the first is less readable perhaps but I think it's more useful for a programmer. To each their own! Maybe some day I'll be convinced otherwise, I like it better for asserts too:

assert(200 = res.statusCode) assert('application/json' == res.headers['content-type'])

assert(res.headers['content-type'] == 'application/json')

looks weird to me now but maybe I'm just used to it

bryanlarsen2• 13 years ago

I often purposefully avoid TJ modules because many of them end up being unmaintained. Before using a TJ project check the outstanding pull requests: are there a large number of open useful looking PR's? Is there somebody besides TJ merging into master: aka has he delegated a maintainer?

jongleberry5• 13 years ago

if there's a project you want to maintain for him, just ask and he'll give you ownership. i help with koa and most of his more popular repos have multiple maintainers now, so don't worry.

tjholowaychuk3• 13 years ago

Ryan left node a long time ago, people still use it, just because the original author isn't involved doesn't make it a bad project

jameswyse2• 13 years ago

There were a few of his projects going this way but he recently reached out for maintainers[1] and things are looking better now.

[1] https://medium.com/code-adventures/c819768a175f

Kiro• 13 years ago

Can someone explain why this is better than for example Express?

ds_10• 13 years ago

One way: It leverages generators, which helps in avoiding callback hell (http://blog.alexmaccaw.com/how-yield-will-transform-node) Koa is written by the same author as express.

untog2• 13 years ago

It's made by the same people who made Express. It seems like it's an off-shoot that uses generators, something that would be difficult to do in Express.

spion2• 13 years ago

Does koa (or co) solve the problem with generators where

* stack traces of errors are useless? [1]

* missing catch filters/pattern matching i.e. catch (e) {} also captures type, reference and range errors i.e. "pokemon exception handling"?

[1] http://spion.github.io/posts/analysis-generators-and-other-a...

jongleberry5• 13 years ago

yes, stack traces work now, as long as they aren't being thrown in a different event loop: https://github.com/koajs/koa/issues/117

spion2• 13 years ago

Oops - I didn't mean thrown errors, I meant errors passed to the callbacks.

It doesn't seem like they are useful yet:

https://gist.github.com/spion/356bfc9cc1089edd2e3b

zimbatm• 13 years ago

What's the star in "function *(){}" for ?

EDIT: Answer: that's how "generator functions" are recognized. http://wiki.ecmascript.org/doku.php?id=harmony:generators

goldenkey• 13 years ago

Thanks, I was wondering the same thing. "A function named star you say?" Heh :-)

vbv• 13 years ago

Does node.js support the * though. I tried their example and getting this:

  app.use(function *(next){
                   ^
  SyntaxError: Unexpected token *
      at Module._compile (module.js:439:25)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Function.Module.runMain (module.js:497:10)
      at startup (node.js:119:16)
      at node.js:901:3

coderzach• 13 years ago

You probably need the `--harmony-generators` or `--harmony` flag.

baudehlo• 13 years ago

It requires node v0.11.3 or above and the --harmony-generators flag at launch.

Or use gnode, which will down-compile it to ES5 for current stable node.

boultonmark• 13 years ago

yawn

http://www.tornadoweb.org/en/stable/gen.html?highlight=gener...

ds_10• 13 years ago

Python has had generators since 2.2, where as they are just landing in js/node.js.

sehr3• 13 years ago

Yeah, strangely enough not all languages/libraries develop functionality at the same time. It's weird, I know.

bottompair• 13 years ago

Python developers always whine about doing their best.

Node developers go home and fuck the prom queen.

turingbook• 13 years ago

Which Nodejs Web framework is the most popular in production? There are so many choices: http://nodeframework.com/

It seems Express and Connect? http://stackoverflow.com/questions/3809539/choosing-a-web-ap...

sehr3• 13 years ago

I'd guess Express. It's in use at quite a few high profile companies, and most other frameworks are just built on top of it.

untog2• 13 years ago

FTA, Koa is made by the same people who make Express.

And Express sits on top of Connect.

prezjordan• 13 years ago

Express is probably the most popular in terms of apps deployed, and sits on top of Connect.

Koa is likely to replace Connect [0].

[0] https://twitter.com/tjholowaychuk/status/369868946989535232

rmrfrmrf2• 13 years ago

It's funny -- I love node.js for pretty much everything except for web frameworks. IMO Express, Koa, Sails, and Meteor are all lacking some kind of je ne sais quoi... maybe I should try my hand at one as an open source project...? Anyone have any good resources about framework design?

cnp2• 13 years ago

Check out Sails.js. It's under active development, but I've used it for a few things and find it totally fantastic:

http://sailsjs.org/

bwilliams3• 13 years ago

I haven't touched it ever since I saw you can create records with GET requests by default. Did they ever fix that?

krsunny3• 13 years ago

Yea Sails is awesome but I feel like the devs have been putting the community on the back burner lately. Its ORM is off to a good start but I find myself writing a bunch of hard to maintain SQL because of the things yet to be implemented, like joins. Also, Windows support could use a ton more testing/attention.

rmrfrmrf2• 13 years ago

lol I listed Sails though--my problem with sails was that their website promised tomes upon tomes of documentation; come to find out the copy on the website is all boilerplate and none of the docs have been completed yet.

tuxie_• 13 years ago

I always felt that I didn't understand the node way of work, because all frameworks feel to me like they are missing something, like they are ignoring the good ideas built in other frameworks. Or maybe they are too functional for my OOP head.

I had to work with express, and one thing that I missed was having a Response object where you build your response and then pass back to the framework at the end of the request. So I built my own proof-of-concept-framework to understand why others don't do it (maybe it was just not possible).

Many people will tell you that there are a thousand frameworks out there, go contribute to one of those instead of creating more noise. For me doing a framework was a great way of learning the internals of node, the kind of things that frameworks are designed to hide away from you. Go for it, start your own open source framework and put your ideas into practice. The ecosystem is still maturing.

rgbrgb• 13 years ago

If anybody finds / does a benchmark, please link it here.

jongleberry5• 13 years ago

there's a silly benchmark in the repo: https://github.com/koajs/koa#benchmarks

but there aren't any comparisons yet.

jongleberry5• 13 years ago

TJ just updated express' benchmarks to match koa's. here are the results on my computer: https://gist.github.com/jonathanong/8065724

Sheepshow• 13 years ago

Not sure I understand the semantics. I'm passed what looks like a continuation, but instead of calling it, I yield it?

What other values can I yield, and why would I want to?

Alternatively, couldn't the `next` object just be a plain continuation?

yojimbo311• 13 years ago